The ocular toxicity of iron (Fe) has been clearly documented in relation to the effects of Fe containing intraocular foreign bodies and hemorrhage. There is now a growing body of evidence which implicates Fe as an integral part of the ocular inflammatory response and associated tissue damage. Much of the work done in the past has centered on histologic and electroretinogram changes induced by Fe. The experiments described in this proposal are designed to integrate biochemical, structural and functional studies of Fe toxicity and to provide new insights into Fe's role in the ocular inflammatory response. The toxic effects of Fe are likely due to its ability to catalyze free radical reactions. Under normal physiologic circumstances, Fe is bound to proteins and cannot catalyze free radical formation. However, Fe can be released from its binding proteins in pathological conditions and can then catalyze these reactions. In an ongoing project in this laboratory methods have been developed for measurement of Fe, total-iron-binding capacity, and "free" catalytic Fe in the intraocular fluids (IOFs) and plasma. In an experimental model, the Fe concentration of the inflamed IOFs was increased more than 20 times that of the uninflamed control eyes. Furthermore, "free" catalytic Fe was found in the inflamed IOFs. In this proposal, the relationship between the presence of "free" Fe and the conditions which increase the likelihood of Fe's release from its binding proteins on parameters of ocular inflammation and tissue damage will be determined using the endotoxin model of ocular inflammation in rabbits. Tissue damage parameters will include changes in electroretinogram, vitreal liquefaction and retinal lipid peroxidation. In a related set of experiments, Fe will be injected intravitreally to determine the threshold level for its damaging effects. The effects of the Fe-chelator desferrioxamine and the endogenous antioxidant Fe-binding protein transferrin will also be explored. In all of the planned experiments the relationship between the amount of "free" Fe in the IOFs, the extent of the inflammatory response and changes in IOF biochemistry and ocular structure and function will be determined. It is likely that further elucidation of Fe's role in the biochemical changes which occur during ocular inflammation will lead to therapeutic advances in the treatment of this ocular pathology.